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Some gases has very low difference between boiling and melting temperatures, like $\Delta T \leq 6~ \text{K}$ :

$$ \text{Helium},~ \{~T_m,T_b\} =\{0.95 K , 4.222 K\} \\ \text{Neon},~ \{~T_m,T_b\} =\{24.56 K , 27.104 K\} \\ \text{Argon},~ \{~T_m,T_b\} =\{83.81 K , 87.302 K\} \\ \text{Hydrogen},~ \{~T_m,T_b\} =\{13.99 K , 20.271 K\} $$

But others starts accumulating more heat, while transitioning to next boiling phase, like $\Delta T \geq 14~ \text{K}$ :

$$ \text{Nitrogen},~ \{~T_m,T_b\} =\{63.15 K , 77.355 K\}\\ \text{Fluorine},~ \{~T_m,T_b\} =\{53.48 K , 85.03 K\} \\ \text{Oxygen},~ \{~T_m,T_b\} =\{54.36 K , 90.188 K\}\\ \text{Chlorine},~ \{~T_m,T_b\} =\{171.6 K , 239.11 K\} $$

Question,- Why first group of gases has comparatively low temperature threshold for transitioning from melting to boiling state ? My gut feeling tells me that it may be somehow related to electron configuration and degrees of freedom, but I'm not able to map exact causes.

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  • $\begingroup$ It would be helpful to have the absolute values of the various melting points for comparison. My first thought looking at these is if a (noble) gas boils at, say, 5K it is not very surprising that its melting point is not far below that. $\endgroup$
    – By Symmetry
    Commented Sep 23, 2021 at 11:07
  • $\begingroup$ Nitrogen boils at $77 K$ and Fluorine boils at $85 K$, so both gases boils below boiling point of Argon (which is $87 K$), but still Argon has lower transitioning temperature difference than these two mentioned above. So there's more interesting stuff should be going on. $\endgroup$
    – Agnius Vasiliauskas
    Commented Sep 23, 2021 at 11:16

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This is more of a chemistry question but anyway in the gases in the first group there are no strong intermolecular forces acting this means that the molecules can easily be seperated. The only forces in the first set are weak vander waal forces. Note that these are not just governing factors most of the time the high melting point indicates ease of being in solid state due to there size and symmetry for example in argon. The low boiling point implies that surface area of liquids is less or molecules are weakly hold together in liquid phase. Whenever a molecule has less surface area and high tendency for close packing tend to have very little difference in there melting and boiling points some times the difference is so small that we see it subliming.

Most important thing is to say is that two different properties determine the melting and boiling points of molecules so you cannot always compare them using one property such degree of freedoms or electronic configuration.

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  • $\begingroup$ I'm almost convinced by your explanation, because if we will skip Argon and Chlorine from the list, then second group of atoms has greater covalent radius, which means that they are able to create a longer bonds between molecules and thus needs more heat to break these stronger bonds and so preserves same structure (liquidity) at higher temperatures. BUT... Argon has covalent radius of $106 pm$- greatest from all mentioned elements, which shows that Argon makes strongest bonds, but still Argon goes faster to boiling than second group elements. So something is not right in your explanation. $\endgroup$
    – Agnius Vasiliauskas
    Commented Sep 23, 2021 at 12:53
  • $\begingroup$ See boiling occurs in a liquid phase covalent radius doesn't define a property of a liquid remember $\endgroup$
    – Soham Patil
    Commented Sep 23, 2021 at 13:39
  • $\begingroup$ Anyway reason why argon's bp is low because it is noble monoatomic gas and there are very weak intermolecular force called vander waal force that is the reason it boils so quickly dont try to use the second part of my answer for noble gases as there are no dipoles and so know other forces they are very loosely held $\endgroup$
    – Soham Patil
    Commented Sep 23, 2021 at 13:43

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